Authoring is a process of designing the application layer format of an optical disc before producing a master optical disc. More specifically, the authoring process involves generating a volume image, which is information having a predetermined format, and recording the volume image on a recording medium. The volume image contains a digital stream compressed and encoded according to the MPEG (Moving Picture Experts Group) standard and also contains a scenario of the digital stream.
Some of authoring processes known in the art are designed for read-only DVDs (generally referred to as “DVD-Video”). When producing an original maser of DVD-Video, an authoring sited does not encrypt the digital stream and scenario. Rather, the authoring site indicates to a mastering site that the digital stream and scenario are requested to be encrypted. Instead of the indication, the authoring site may simply provide a key to be used for the encryption. In either case, the encryption is carried out by the mastering site not by the authoring site. That is to say, the volume image formatted for DVD-Video is non-encrypted. The reason for not encrypting at the authoring site is that the encryption system generally employed for DVD-Video is CSS (content scramble system) according to which the data size remains the same before and after the encryption. In addition, it is more efficient to perform the encryption at the mastering site. If the encryption is performed at the authoring site, the mastering site is required to go through a decryption process in order to verify the encrypted data.
Unfortunately, however, data encrypted by CSS is readily decryptable once a correct key is obtained and thus the copyright protection provided by CSS may not be sufficient.
For read-only Blu-ray Disc ROM (hereinafter “BD-ROM”) that are expected to be available in the near future, AACS (advanced access content system) is employed for encryption in order to provide more robust copyright protection. AACS provides robust protection by various functions, including addition of a hash value, use of a signature, and device revocation.
See Patent Document 1: WO2005/002232